26
D. Gregurek et al.
with iron oxide. This is most frequently observed in magnesia-chromite bricks from
the short rotary furnace where iron scrap is used as reducing agent in the processing
of lead batteries.
As can be seen from the chemical analysis, up to 26 wt% of Fe 2 O 3 (respectively
23.4 wt% FeO) can be determined (Table 2).
The high iron oxide supply results in degeneration of the brick microstructure and
formation of Mg–Fe–oxide of magnesia-wuestite type (Fig. 5).
Non-oxide Infiltration
In addition to acidic slag, also other components like metallic lead, PbS, etc. infiltrate
the brick microstructure. Generally, non-oxide infiltration only densifies the bricks
microstructure without any corrosive attack on the brick components. Similar to the
acidic slag, the degree of infiltration depends on the surface tension, the boundary
angle in contact with the refractory oxides, the temperature, the bath height, and the
size/distribution of the brick pores [14].
Microstructural Changes Due to High Temperature Load
Although the temperatures in lead furnaces are typically well below the maximum
service temperature of the as-delivered refractory materials, the temperature plays
an important role in the continuous wear of the bricks. The higher degradation rate
caused by the reduced viscosity and higher diffusivity associated with an overheated
melt clearly demonstrates the effect of temperature.
On the microscopic level, a very characteristic feature for this wear phenomenon
is periclase crystal growth and lengthening towards the thermal gradient resulting
in several mm long crystals. The crystal size of the single periclase crystals within
the original sintered magnesia is usually up to 140 µm [13]. However, in highly
degenerated brick microstructure, the single grains, as well as the classical ceramic
microstructure with coarse grains and matrix fines, cannot be observed anymore;
thus, they have grown into one big crystal. In addition to this, also the supplied
oxide components such as zinc-, iron-, and tin-oxide act as mineralizing agents, thus
strongly supporting the periclase crystal growth.
Such microstructural changes are typical for ferroalloy furnaces where the operating temperature is much higher than in base metal production. So far in lead processing, this wear phenomenon was observed in the KIVCET furnace only due to
the high furnace operation temperature.
D. Gregurek et al.
with iron oxide. This is most frequently observed in magnesia-chromite bricks from
the short rotary furnace where iron scrap is used as reducing agent in the processing
of lead batteries.
As can be seen from the chemical analysis, up to 26 wt% of Fe 2 O 3 (respectively
23.4 wt% FeO) can be determined (Table 2).
The high iron oxide supply results in degeneration of the brick microstructure and
formation of Mg–Fe–oxide of magnesia-wuestite type (Fig. 5).
Non-oxide Infiltration
In addition to acidic slag, also other components like metallic lead, PbS, etc. infiltrate
the brick microstructure. Generally, non-oxide infiltration only densifies the bricks
microstructure without any corrosive attack on the brick components. Similar to the
acidic slag, the degree of infiltration depends on the surface tension, the boundary
angle in contact with the refractory oxides, the temperature, the bath height, and the
size/distribution of the brick pores [14].
Microstructural Changes Due to High Temperature Load
Although the temperatures in lead furnaces are typically well below the maximum
service temperature of the as-delivered refractory materials, the temperature plays
an important role in the continuous wear of the bricks. The higher degradation rate
caused by the reduced viscosity and higher diffusivity associated with an overheated
melt clearly demonstrates the effect of temperature.
On the microscopic level, a very characteristic feature for this wear phenomenon
is periclase crystal growth and lengthening towards the thermal gradient resulting
in several mm long crystals. The crystal size of the single periclase crystals within
the original sintered magnesia is usually up to 140 µm [13]. However, in highly
degenerated brick microstructure, the single grains, as well as the classical ceramic
microstructure with coarse grains and matrix fines, cannot be observed anymore;
thus, they have grown into one big crystal. In addition to this, also the supplied
oxide components such as zinc-, iron-, and tin-oxide act as mineralizing agents, thus
strongly supporting the periclase crystal growth.
Such microstructural changes are typical for ferroalloy furnaces where the operating temperature is much higher than in base metal production. So far in lead processing, this wear phenomenon was observed in the KIVCET furnace only due to
the high furnace operation temperature.